The present invention relates to an implantable automatic defibrillator and more particularly to a feature in an implantable automatic defibrillator for diverting the charge on a defibrillator capacitor to an internal load.
In implantable cardiac treatment devices, such as an implantable defibrillator, a cardiac arrhythmia is detected based on sensed electrical and other activity of the heart. In defibrillation, the determination of a tachycardia, or fast beating heart, is indicative of impending ventricular fibrillation. Upon the determination of such an arrhythmia, a defibrillation capacitor is charged to a selected level for ultimately discharging and delivering an electrical shock to the heart.
Oftentimes, the arrhythmia of the heart is temporary and does not further develop into fibrillation, but reverts to normal sinus rhythm. This can occur while the defibrillation capacitor is charging or shortly after the capacitor has been charged. If the capacitor is discharged to a heart in normal sinus rhythm, the result could be detrimental, and at the worst put the heart into an arrhythmia. In addition, a high energy defibrillation shock normally causes some trauma to the patient; thus an unnecessary shock is to be avoided.
To avoid delivering an unnecessary defibrillation shock, it would be advantageous to delay the discharge of the defibrillation capacitor after it has been fully charged to allow further monitoring if there is an indication that the arrhythmia has reverted to normal sinus rhythm during the charging process.
Some defibrillation devices incorporate delays for manually disenabling the capacitor discharge. See for example U.S. Pat. Nos. to Bradley et al. (4,576,170) and Heilman et al. (4,210,149). These devices have built-in delays to allow the wearer to disenable the implantable device to prevent the delivery of a shock after the patient is audibly warned of an impending shock. The purpose of these devices is to allow the patient to override the implantable device in the event that a false detection occurs.
These devices fail in that a truly accurate examination of the heart activity is not made when disenabling the device. Therefore, it is possible to ignore a malignant heart condition.